Radiation-curing coating systems

ABSTRACT

Radiation-curing coating systems which contain a silanized silica, where the silane is hexamethyldisilazane, 3-methacryloxypropyltrialkoxysilane and/or glycidyloxypropyltrialkoxysilane as the silanizing agent. The radiation-curing coating systems can be used for coating derived timber boards, solid wood, wood veneers, parquet, decorative papers, decorative films, thermoplastics and thermosetting plastics, mineral and polymeric glasses, metals (for example aluminium, high-grade steel, phosphated, chromated and galvanized steel sheets, copper), lacquered surfaces, printing inks and leather.

INTRODUCTION AND BACKGROUND

[0001] The present invention relates to radiation-curing coating systems, a process for their preparation and their use.

[0002] Radiation-curing coating systems are used to coat surfaces of wood, metals and plastics.

[0003] In some formulations the known radiation-curing coating systems have the disadvantage that the surface hardness is inadequate.

[0004] It is therefore an object of the present invention to develop radiation-curing coating systems which do not have these disadvantages.

SUMMARY OF THE INVENTION

[0005] The above and other objects of the present invention can be achieved by radiation-curing coating systems, which are characterized in that they comprise at least one silanized silica, where a silane from the group consisting of hexamethyldisilazane, 3-methacryloxypropyltrialkoxysilane and/or glycidyloxypropyltrialkoxysilane is used as the silanizing agent.

[0006] In a preferred embodiment of the invention, the silanized silica can be structurally modified. A silica such as described in the document EP 0 808 880 A2 can be used as the silanized silica. This document is incorporated herein by reference. The silica according to EP 0 808 880 A2 is a silanized silica with the following physico-chemical properties: Specific surface area (BET) m²/g 80-400 Primary particle size nm 7-40 Tamped density g/l 50-300 pH 3-10 Carbon content % 0.1-15   DBP (dibutylphthalate) number % <200

[0007] This silanized silica is prepared by a process in which a silica is sprayed optionally first with water or dilute acid and then with a surface modification reagent or a mixture of several surface modification reagents in a suitable mixing vessel, with intensive mixing, the components are re-mixed for 15 to 30 minutes and heat-treated at a temperature of 100 to 400° C. over a period of 1 to 6 h, and the silanized silica is then destructured/compacted by mechanical effects and re-ground in a mill.

[0008] A silica prepared pyrogenically by the route of flame hydrolysis of SiCl₄ can preferably be employed as the silica. Hexamethyldisilazane, for example, can be employed as the surface modification reagent.

[0009] The coating according to the invention which can be cured by radiation comprises a reactive binder which contains double bonds in the terminal position or in the β-position relative to a reactive group which can be polymerized by free radicals. The double bonds can cure or polymerize under the influence of UV light or electrons. Copolymerizable reactive thinners (monomers) can be used to lower the viscosity.

[0010] Further components can be fillers, flatting agents and/or pigments. If required, wetting agents, flow control and degassing agents and other additives can be used in radiation-curing systems.

[0011] In UV technology, photoinitiators or photosensitizers are used to initiate the polymerization. In the case of curing by electron beams, the high-energy radiation itself forms the initiator radicals for the polymerization reaction.

[0012] The invention also provides a process for the preparation of the radiation-curing coating systems according to the invention, which is characterized in that 1 to 20%, preferably 2 to 10% of silanized pyrogenic silica, depending on the rheology of the system, is stirred into the coating system.

DETAILED DESCRIPTION OF INVENTION

[0013] The coating systems according to the invention can be used for coating a wide variety of surfaces such as derived timber boards, solid wood, wood veneers, parquet, decorative papers, decorative films, thermoplastics and thermosetting plastics, mineral and polymeric glasses, metals (for example aluminium, high-grade steel, phosphated, chromated and galvanized steel sheets, copper), lacquered surfaces, surfaces coated with printing inks and leather.

[0014] The radiation-curing coating systems according to the invention have the following advantages:

[0015] Improvement in the surface hardness, in particular scratch resistance, without impairment of the application properties, and in the optical properties of the crosslinked coating films.

[0016] According to the invention, the pyrogenically prepared silicas according to table 1 can be employed as the silica for the silanization. AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL Test method 90 130 150 200 300 380 OX 50 TT 600 Behaviour towards hydrophilic water Appearance loose white powder Bet surface area¹⁾ m²/g 90 ± 15 130 ± 25 150 ± 15 200 ± 25 300 ± 30 380 ± 30 50 ± 15 200 ± 50 Average primary Nm 20 16 14 12 7 7 40 40 particle size Tamped density g/l 80 50 50 50 50 50 130 60 approx. values²⁾ compacted goods g/l 120 120 120 120 120 120 (added “V”) VV goods g/l 50/75 50/75 50/75 (added “VV”)¹²⁾ g/l 120 120 Loss on drying³⁾ % <1.0 <1.5 <0.5⁹⁾ <1.5 <1.5 <2.0 <1.5 <2.5 (2 hours at 105° C.) on leaving supply works Loss on ignition⁴⁾⁷⁾ % <1 <1 <1 <1 <2 <2.5 <1 <2.5 (2 hours at 1000° C.) pH⁵⁾ 3.7-4.7 3.7-4.7 3.7-4.7 3.7-4.7 3.7-4.7 3.7-4.7 3.8-4.8 3.6-4.5 SiO₂ ⁸⁾ % >99.8 >99.8 >99.8 >99.8 >99.8 >99.8 >99.8 >99.8 Al₂O₃ ⁸⁾ % <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.08 <0.05 Fe₂O₃ ⁸⁾ % <0.003 <0.003 <0.003 <0.003 <0.003 <0.003 <0.01 <0.003 TiO₂ ⁸⁾ % <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 HCI⁸⁾¹⁰⁾ % <0.025 <0.025 <0.025 <0.025 <0.025 <0.025 <0.025 <0.025 Sieve residue⁸⁾ % <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.2 <0.05 (Mocker method, 45 μm) Drum size (net)¹¹⁾ Kg 10 10 10 10 10 10 10 10

EXAMPLES Example 1

[0017] A silanized silica is prepared in accordance with example 1 of EP 0 808 880 A2. Aerosil® 200 (silica) is mixed with 4.3 parts water and 18.5 parts HMDS (hexamethyldisilazane) and the mixture is heat-treated at 140° C. The silanized silica is then compacted to approx. 250 g/l on a continuously operating vertical ball mill. Thereafter, the silica is re-ground by means of an air jet mill. The silica obtained has the following properties: Loss on Loss on DBP BET Tamped drying ignition number Example m²/g density pH C content % % % VT 145 188 7.3 2.7 2.4 0.3 90 1128/1

Example 2

[0018] Aerosil® 200 is mixed with 4 parts water and 18 parts 3-methacryloxypropyltrimethoxysilane and the mixture is heat-treated at 140° C. under an inert gas. The silanized silica is then compacted to approx. 250 g/l on a continuously operating vertical ball mill. The silica obtained has the following properties: BET [m²/g] 138 Tamped density [g/l] 242 pH  4.6 C content  5.7 Loss on drying [%]  0.6 Loss on ignition [%]  8.9 DBP number [%] 122

[0019] Experiments with silica according to example 2 in UV-curing binders:

[0020] Experiment 1

[0021] 10% silica according to example 2 are stirred into the binder (ethoxylated pentaerythritoltetracrylate), with a dissolver and then predispersed for 5 min at 3000 rpm (discØ45 mm). The mixture is dispersed in a laboratory bead mill for 20 min at 2500 rpm and a pump output of 40%. 1 mm glass beads are used as the beads. The dispersing quality is checked with a grindometer, 25 μm, in accordance with DIN ISO 1524. It must be smaller than 10 μm.

[0022] 3% photoinitiator is stirred into the coating. Application is carried out with the aid of a spiral doctor blade (amount applied 36 μm) on black-lacquered metal sheets. Curing is carried out with a UV unit (current uptake of the UV lamp (mercury vapour lamp) 7.5-10 mA, belt speed 10 m/min, irradiation intensity 1 W/cm).

[0023] Experiment 2

[0024] 10% silica according to example 2 are stirred into the binder 2 (Epoxyacrylate A) with a dissolver and then predispersed for 5 min at 3000 rpm (discØ45 mm). The mixture is dispersed in a laboratory bead mill for 15 min at 2500 rpm and a pump output of 40%. 1 mm glass beads are used as the beads. The dispersing quality is checked with a grindometer, 25 μm, in accordance with DIN ISO 1524. It must be smaller than 10 μm.

[0025] 3% photoinitiator is stirred into the coating. Application is carried out with the aid of a spiral doctor blade (amount applied 36 μm) on black-lacquered metal sheets. Curing is carried out with a UV unit (current uptake of the UV lamp (mercury vapour lamp) 7.5-10 mA, belt speed 10 m/min, irradiation intensity 1 W/cm)

[0026] Experiment 3

[0027] 16% silica according to example 2 are stirred into the binder 3 (Epoxyacrylate B) with a dissolver and then predispersed for 5 min at 3000 rpm (discØ45 mm). The mixture is dispersed in a laboratory bead mill for 15 min at 2500 rpm and a pump output of 40%. 1 mm glass beads are used as the beads. The dispersing quality is checked with a grindometer, 25 μ, in accordance with DIN ISO 1524. It must be smaller than 10 μm.

[0028] 3% photoinitiator is stirred into the coating. Application is carried out with the aid of a spiral doctor blade (amount applied 36 μm) on black-lacquered metal sheets. Curing is carried out with a UV unit (current uptake of the UV lamp (mercury vapour lamp) 7.5-10 mA, belt speed 10 m/min, irradiation intensity 1 W/cm). TABLE 1 Grindometer values, Brookfield viscosities: Viscosity Grindo-meter [mPa s] SV value [μm] 6 rpm 60 rpm 6/60 binder 1 — 160 158 1.0 binder 1 + silica <10 451 389 1.1 according to example 2 binder 2 — 481 468 1.0 binder 2 + silica <10 1,000   950 1.1 according to example 2 binder 3 — 521 494 1.1 binder 3 + silica <10 902 842 1.1 according to example 2

[0029] Scratching Experiments

[0030] The metal sheets are scoured with a quartz/water slurry (100 g water+1 g Marlon A 350, 0.25%+5 g Sikron F500) with 100 strokes with the aid of a scouring and washing resistance testing machine (Erichsen). The shine before and 10 min after scouring is determined with a reflectometer (20° incident angle). TABLE 2 Reflectometer values before and after scratching: 20° reflectometer value Residual before after shine [%] binder 1 82.0 50.0 61.0 binder 1 + silica 80.5 65.2 81.0 according to example 2 binder 2 89.6 46.5 51.9 binder 2 + silica 87.8 67.4 76.8 according to example 2 binder 3 88.9 62.0 69.7 binder 3 + silica 87.3 71.4 81.8 according to example 2

Example 3

[0031] Aerosil® 200 is mixed with 4 parts water and 18 parts 3-methacryloxypropyltrimethoxysilane (for example DYNASILAN MEMO) and the mixture is heat-treated at 140° C. under an inert gas. The silica obtained has the following properties: BET [m²/g] 138 Tamped density [g/l]  52 pH  4.6 C content  5.7 Loss on drying [%]  0.8 Loss on ignition [%]  9.7 DBP number [%] 228

Example 4

[0032] Aerosil® 200 is mixed with 3 parts water and 16 parts 3-glycidyloxypropyltrimethoxysilane (for example DYNASILAN GLYMO) and the mixture is heat-treated at 140° C. under an inert gas.

[0033] The silica obtained has the following properties: BET [m²/g] 165 Tamped density [g/l]  53 pH  4.9 C content  5.5 Loss on drying [%]  1.5 Loss on ignition [%]  8.7 DBP number [%] 242

[0034] Further variations and modifications of the foregoing will be apparent to those skilled in the art and are intended to be encompassed by the claims appended hereto.

[0035] European priority application 00 122 956.6 of Oct. 21, 2000 is relied on and incorporated herein by reference. 

We claim:
 1. A radiation-curing coating composition comprising, at least one silanized silica, where a silane selected from the group consisting of hexamethyldisilazane, 3-methaeryloxypropyltrialkoxysilane, glycidyloxypropyltrialkoxysilane, and mixture thereof is used to form the silanized silica, and polymerizable reactive binder containing double bonds.
 2. The radiation-curing coating compositions according to claim 1, characterized in that the silanized silica is structurally modified.
 3. The radiation-curing coating compositions according to claim 1 which has a grindometer value of less than 10 μm.
 4. A process for the preparation of the radiation-curing coating composition according to claim 1, comprising stirring into the coating composition 1-20% silanized pyrogenic silica.
 5. A process for the protection of a surface comprising coating a surface with the composition of claim 1 and subjecting the surface to radiation-curing to produce a cured coating on said surface. 